Continuum fluids with a discontinuity in the pressure

A class of one-dimensional continuum fluid models is defined in which classical particles interact through translationally invariant, strongly tempered manybody potentials meeting conditions sufficient to ensure a proper thermodynamic limit. However, an exact analysis demonstrates that for certain ranges of parameter values the pressure versus density isotherms arediscontinuous. The basic models also entail discontinuous temperature versus configurational entropy isobars but extended models are described which exhibit either type of anomaly alone and various unobserved but thermodynamically allowed, anomalous types of first-order transitions.     

Abrupt discontinuity of the bulk modulus pressure dependence in Fe64Ni36

X-ray diffraction and ultrasonic measurements have been carried out simultaneously up to 7 GPa at ambient temperature on a polycrystalline sample of Fe64Ni36 Invar alloy. The bulk modulus is found to increase linearly with pressure with an unusual low value (1.4) of dB/dP up to about 3.1(2) GPa followed by a regular slope (3.6) at higher pressure. The observation of these two distinct regimes is in qualitative agreement with previous results on the variation of the iron magnetic moment, and can be interpreted using the 2gamma-state model in terms of gradual population of low spin-small volume state at the expense of the high spin-large volume state under pressure.     

On the length of a discontinuity in an acoustically active medium

The discontinuity length is found when a high-frequency gasdynamic perturbation propagates in a thermodynamically nonequilibrium gaseous medium.     

On discontinuity and tail behaviours of the integrated density of states for nested pre-fractals

We consider a general finitely ramified fractal set called a nested fractal which is determined byN number of similitudes. Basic properties of the integrated density of statesN (x) for the discrete Laplacian on the associated nested prefractal are investigated. In particulard N is shown to be purely discontinuous ifM, whereM is the number of branches of the inverse of the rational function involved in the spectral decimation method due to Rammal-Toulouse. Sierpinski gaskets and the modified Koch curve are special examples.     

On the heat capacity discontinuity for a gas of nuclear spin waves in ferromagnets

It is demonstrated that the heat capacity discontinuity for a gas of nuclear spin waves occurs in ferromagnetic materials. The heat capacity discontinuity manifests itself at ultralow temperatures and stems from the specific spectrum of these quasiparticles. The effect is observed at the temperature T _K?2.37?ω_n. The heat capacity discontinuity is found at this temperature.     

Analysis of planar waveguides with index discontinuity or index slope discontinuity

In this paper, we propose a novel analytic transfer matrix method (ATMM) to the analysis of planar waveguides with index discontinuity or index slope discontinuity, for the cases when the conventional WKB method is no longer valid. We also analyze the physical insight of the approximations in WKB theory, and according to our research, the phase shift at the turning point is not /2, but exactly . Test calculations are done for an index profile with a known solution and the comparison shows that our method gives extremely accurate propagation constant.     

Hamilton-Jacobi theory for continuation of magnetic field across a toroidal surface supporting a plasma pressure discontinuity

The vanishing of the divergence of the total stress tensor (magnetic plus kinetic) in a neighborhood of an equilibrium plasma containing a toroidal surface of discontinuity gives boundary and jump conditions that strongly constrain allowable continuations of the magnetic field across the surface. The boundary conditions allow the magnetic fields on either side of the discontinuity surface to be described by surface magnetic potentials, reducing the continuation problem to that of solving a Hamilton-Jacobi equation. The characteristics of this equation obey Hamiltonian equations of motion, and a necessary condition for the existence of a continued field across a general toroidal surface is that there exist invariant tori in the phase space of this Hamiltonian system. It is argued from the Birkhoff theorem that existence of such an invariant torus is also, in general, sufficient for continuation to be possible. An important corollary is that the rotational transform of the continued field on a surface of discontinuity must, generically, be irrational.     

On the resonance light pressure

An expression for the resonance radiation pressure is found in the framework of the Weisskopf-Wigner theory. It is shown, that at saturation its value is twice that of the phenomenological theory.     

On the pressure of gravitational waves

A system of coupled point masses under the influence of gravitational waves is considered. By means of the geodesic deviation equation as the equation of motion it is shown, taking into account the second order small terms, that there exist forces which cause the acceleration of the system in the longitudinal direction. The longitudinal force is due to the fact that simultaneously with energy momentum is also absorbed from waves. It is proved directly on the basis of the equations of motion of the point masses that the energy and momentum absorbed by the test system obey the special relativistic relationship of a zero rest mass particle. The case when the Weber oscillator moves at a relativistic speed with respect to the source of gravitational waves is also examined. In this case, the absorption of energy and momentum by the Weber oscillator is much larger or smaller compared to the stationary situation.     

Instabilities of a tangential discontinuity

A critical analysis of Landau and Lifshitz’s data concerning the instability of a tangential discontinuity in a compressible liquid is given. The simplest case when the liquid flow velocity alone experiences a discontinuity is considered. The influence of a high transverse gravitational field on the stability of a tangential discontinuity is investigated.     

On the accuracy of oxygen pressure measurements

Zirconia-based oxygen sensors are used in many applications and in research. However, the measurement of oxygen partial pressures with these devices is not necessarily correct. Reasons for deviation between sensor reading and nominal composition of the gas mixture are reviewed in this work. The sensor electrochemical permeability is introduced as a starting point. The impact of this oxygen leak on the composition of the surrounding atmosphere is evaluated from mass balances to all species in the system. This procedure shows that even the use of mixtures like CO+CO₂ to establish a given oxygen partial pressure has a limited range of applicability. This is due to the small buffer behavior of some of these mixtures. The gas phase transport of oxygen away from the sensor electrode is also studied. High concentration overpotentials are expected to develop under the circumstances where the buffer behavior of the gas mixture is small. In fact, high concentrations of the CO/CO₂ couple are required both to optimize the gas-mixture buffer effect and the oxygen transport in the gas phase. The latter instead of consisting exclusively of simple diffusion of free oxygen molecules might also involve combined diffusion and counter diffusion of both carbon oxides as oxygen carriers.     

On the behaviour of TSeF-TCNQ under pressure

We report b-axis electrical conductivity data for TSeF-TCNQ single crystals from 12 to 300 K under hydrostatic pressures up to 9 kbar. The single anomaly visible in the conductivity at 29 K and the low temperature conductivity gap rise under pressure at the same rate of ～ 6% kbar^-1. It has been found that the pressure dependence of the metal-insulator phase transition is qualitatively consistent with a mean field formulation of the Peierls transition. A Gruneisen constant of 0.64 for TSeF-TCNQ has been derived from this pressure study together with recent optical and compressibility investigations. The pressure dependence of the conductivity anisotropies at room temperature in TSeF-TCNQ and TTF-TCNQ are reported. The magnitude of the anisotropies in the two compounds are found to be essentially the same. The striking result, however, is that the anisotropies in both compounds are found to be independent of pressure up to 9 kbar.     

On the origin of discontinuity of the hyperfine fields at Fe nuclei in bulk iron and aerosol Fe nanoparticles

Advancing the early work in which a discontinuity of hyperfine fields at ⁵⁷Fe nuclei in bulk iron and in aerosol Fe nanoparticles has been revealed by analyzing their Mössbauer spectra the present Letter evidences that the existence of several peaks in the hyperfine distribution (HFD) for bulk Fe is caused with the internal magnetic fields owing to its multidomain structure whereas aerosol Fe nanoparticles are single-domain and show only a unique peak in HFD. This argument has been corroborated by transformation of the HFD pattern for Fe foil after applying the external magnetic field of 0.03 T.     

Modelling of structures with developing discontinuity

Discontinuity is one of the most important factors which contribute to the nonlinearity, challenging both methods of nonlinear analysis and its application for the analysis of interacting mechanical processes. The problem becomes more complicated when the discontinuity is developing under the influence of dynamic processes in the structures. This paper presents the methodology for analysis and simulation of the systems with the developing discontinuity based on the combination of analytical technique and the Matlab–Simulink computation. As an example, model of a cracked bar subjected to longitudinal excitation is used to analyse a nonlinear response as a way to monitor structural health. Different strategies of monitoring are compared based on the tracking the qualitative transformation of the bar?s vibration.     

论声压级平均算法

本文阐述了求声压级平均值的几种算法,特别论述了对声压级数据直接进行算术平均的运算方法。     

On the role of pressure in elasto-inertial turbulence

The dynamics of elasto-inertial turbulence is investigated numerically from the perspective of the coupling between polymer dynamics and flow structures. In particular, direct numerical simulations of channel flow with Reynolds numbers ranging from 1000 to 6000 are used to study the formation and dynamics of elastic instabilities and their effects on the flow. Based on the splitting of the pressure into inertial and polymeric contributions, it is shown that the polymeric pressure is a non-negligible component of the total pressure fluctuations, although the rapid inertial part dominates. Unlike Newtonian flows, the slow inertial part is almost negligible in elasto-inertial turbulence. Statistics on the different terms of the Reynolds stress transport equation also illustrate the energy transfers between polymers and turbulence and the redistributive role of pressure. Finally, the trains of cylindrical structures around sheets of high polymer extension that are characteristics of elasto-inertial turbulence are shown to be correlated with the polymeric pressure fluctuations.     

On the mechanism of the zircon-reidite pressure induced transformation

We report first principles results of a detailed investigation directed to elucidate mechanistic aspects of the zircon-reidite phase transition in ZrSiO₄. The calculated thermodynamic boundary is located around 5 GPa, and the corresponding thermal barrier, estimated from temperatures at which the transition is observed at zero and high pressure, is 133 kJ/mol. Under a martensitic perspective, we examine two different transition pathways at the thermodynamic transition pressure. First, the direct, displacive-like, tetragonal I4₁/a energetic profile is computed using the c/a ratio as the transformation parameter, and yields a very high activation barrier (236 kJ/mol). Second, a quasi-monoclinic unit cell allows us to characterize a transition path from zircon (β=90^°) to reidite (β=114.51^°) with an activation barrier of around 80 kJ/mol at β=104^°. This energy is somewhat lower than our previous estimation and supports the reconstructive nature of the transformation at the thermodynamic transition pressure.     

On the definition of the pressure of an infinite system

A microcanonical system $\text{L}$^o_Λ is considered together with a manometer $\text{M}$_Λ. The thermodynamic limit Λ → ∞ is taken for the system $\text{L}$_Λ composed of $\text{L}$^o_Λ and $\text{M}$_Λ. This yields a definition of the pressure P(v, ε) of $\text{{}\text{L}{}^{\mathrm{o}}{}_{\mathrm{\Lambda }}\text{; Λ → ∞}}$ for given values ε and v of the energy and particle densities. P(v, ε) is shown to be equal to the thermodynamic function p(z, β) derived from the grand canonical ensemble for almost all values of ε and v provided the appropriate equilibrium values of the temperature β^?1 and the chemical potential μ = β^?1 log z are inserted.